Soil active organic carbon components, enzyme activities, and microbial nutrient limiting characteristics of Moso...

Fertilization is an effective practice for improving soil fertility and enhancing aboveground productivity. We conducted an experiment with five fertilization treatments at the Northwest Zhejiang Bamboo Forest Ecosystem Positioning Observation and Research Station, including compound fertilizer (NPK), silkworm organic fertilizer (SEOF), microbial organic fertilizer (MOF), silkworm organic fertilizer combined with compound fertilizer (SNPK), and microbial organic fertilizer combined with compound fertilizer (MNPK), with no fertilization as control (CK). We investigated basic soil chemical properties, active organic carbon components, enzyme activities, and enzyme stoichiometric ratios, and identified the main factors affecting enzyme activities and stoichiometric ratios under different fertilization modes. The results showed that fertilization treatments significantly increased the contents of soil organic carbon (SOC), total nitrogen, total phosphorus, alkali-hydrolyzable nitrogen (AN), and available phosphorus by 24.5%-85.4%, 4.0%-59.0%, 15.6%-75.0%, 2.3%-37.7%, and 9.3%-1520.5%, respectively. SEOF, MOF, SNPK, and MNPK treatments significantly increased soil dissolved organic carbon and particulate organic carbon contents by 16.5%-62.4% and 10.6%-82.8%, respectively. SNPK and MNPK treatments significantly increased soil easily oxidizable organic carbon (ROC) content by 37.8% and 10.5%, respectively, while SEOF and MOF treatments significantly decreased ROC content. SNPK and MNPK treatments significantly enhanced the activities of β-1,4-glucosidase (BG) and acid phosphatase. SEOF and MOF treatments significantly increased the activities of β-1,4-N-acetylglucosamine glucosidase and leucine aminopeptidase. SNPK and MNPK treatments significantly increased the stoichiometric ratios of carbon- and nitrogen-acquiring enzymes (C:N_EEA) and carbon- and phosphorus-acquiring enzymes (C:P_EEA), while significantly decreased the stoichiometric ratio of nitrogen- and phosphorus-acquiring enzyme (N:P_EEA). In contrast, SEOF and MOF significantly decreased the stoichiometric ratio of C:N_EEA. All fertilization treatments significantly increased aboveground biomass of new bamboo by 61.1%-94.7%. The enzyme stoichiometry vector model revealed that soil microorganisms treated with NPK, SNPK, and MNPK were co-limited by C and P, while soil microorganisms treated with CK, SEOF, and MOF treatments were primarily limited by P. Moreover, the SEOF and MOF significantly alleviated microbial C and P limitations compared to the SNPK and MNPK treatments. Correlation analysis and redundancy analysis (RDA) demonstrated that SOC and ROC were significantly positively correlated with BG, C:N_EEA, and C:P_EEA, but significantly negatively correlated with N:P_EEA. AN was identified as the most important factor driving soil active organic carbon fractions and new bamboo growth. In summary, the application of organic fertilizer alone and the combined application of organic fertilizer and compound fertilizer significantly increased soil active organic carbon components, nutrient contents, and enzyme activity, and alleviated microbial C and P limitations. Among all treatments, the combination of silkworm organic fertilizer with compound fertilizer (SNPK) achieved the optimal effect on bamboo yield.